As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RT PROPELLER OIL TEMPERATURE FLUCTUATES IN FLIGHT. FLUCTUATES FROM APPROXIMATELY 100 DEGREESTO 150 DEGREES CELSIUS. NORMAL INDICATION ON GROUND. AIR TURNBACK TO DTW. MAINTENANCE REPLACED PGB TEMP BULB WITH SERVICEABLE IAW AMM PN ON/OFF 4053T73P01. OPS AND SECURITY CHECK GOOD AT THE TIME.